In gasoline engines, an air/fuel mixture is ignited within a cylinder by a spark from a spark plug. Spark plugs of an engine may become fouled, preventing the engine from starting and/or increase cranking during starting. Two examples of spark plug fouling are carbon fouling and wet fouling. Carbon-fouled spark plugs have increased carbon build-up on an electrode of the spark plug. Wet-fuel fouled spark plugs are caused by liquid fuel buildup around the electrode, also known as engine flooding. An engine may flood due to rich fueling during extreme temperature-related weather conditions, because of a short engine operation after engine start, when operators depress/pump the gas pedal repeatedly during cranking, or due to excess fuel inside the cylinders. When an engine floods, the spark plugs become wet and cannot produce a spark at the electrode, thus delaying or preventing engine start. In some instances, engine flooding may cause a frustrated vehicle operator to continue cranking the engine until the battery drains.
U.S. Pat. No. 8,150,604 discloses a method to reduce spark plug fouling by making a determination of a spark plug fouling condition by an engine controller from information collected from a number of sensors probing the engine system. Once this method determines a fouling condition, it adjusts one of a number of engine operation parameters such as shutting-off fuel injection during cranking conditions, warming up the engine at a an increased rate that is faster than a normal engine warm-up rate, and reducing the amount of fuel provided to the engine during the initial cranking or start-up of the engine.
However, the inventors herein have recognized an issue with the above approach. While the mechanisms described in U.S. Pat. No. 8,150,604 may help delay or prevent future spark plug fouling, no solutions are provided to rapidly mitigate spark plug wet-fouling after it has already occurred. While wet-fouled spark plugs will eventually dry over time, or they can be removed and dried with compressed air or with a heat gun, such methods are either intrusive or time consuming. Accordingly, the inventors offer a method to at least partly address the above issues. In one embodiment, a method for an engine system is disclosed comprising, responsive to detecting spark plug fouling prior to an engine start, transferring heat to a gas in the engine system, and flowing the heated gas through one or more cylinders of an engine while the engine is not rotating. In this way, once wet-fouling of a spark plug is detected, a plurality of engine operating parameters may be adjusted to direct the flow of heated air through the cylinders of an engine to evaporate the liquid fuel fouling the spark plugs. The detection of the wet-fouling of a spark plug may comprise, in one example, the detection of a throttle position during engine cranking of the prior engine start attempt, or in another example, the detection of a threshold number of prior engine start attempts being reached. The heated air flowing through one or more cylinders of the engine may comprise flowing one or more of heated fuel vapors and heated fresh air from an evaporative emission control (EVAP) system through the one or more cylinders of the engine.
The current disclosure describes a method to perform spark plug drying in-situ using the enhanced evaporation rates afforded by forced convection. By pumping hot air through the cylinder, the fuel may evaporate and be carried away into the exhaust system of an engine at a rate that may be faster than that obtained when the fuel on the spark plugs is allowed to evaporate by the effect of natural convection currents.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.